This isn't normal. There is a rattling of sort, it's either a loose bolt of sump guard/bracket or come what may. Have you installed an after market sump guard? When was the bike last serviced, and do you have the right oil level?
Seems it's not from inside the engine. It's like a bolt is loose, exhaust maybe? Or maybe something inside the exhaust is broken. Hit the exhaust while engine is turned of and cold.
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